The Fortress Language Specification - CiteSeerX

Fortress.IO
Fortress.Crypto
IronIO
IronCrypto
Fortress.IO
Fortress.Security
Figure 22.1: Simple components in box notation: A component is represented by a box, with the name of the component
at the top of the box. The arrow protruding from the upper right corner of a box is labeled with the APIs exported
by the component. The arrow pointing into the bottom of a box is labeled with APIs imported by the component. If
no APIs are imported, we elide the arrow.
Compile This operation takes the source code for a simple component (or API) definition and produces a new
component object (or API object) that is installed on the fortress. Its type is as follows:
compile(file:String):()
For example, suppose IronCrypto.fss contains the source code for the aforementioned IronCrypto application,
which imports Fortress.IO and Fortress.Security, and exports Fortress.Crypto. Suppose we also have source code,
IronIO.fss, for another application, IronIO, which imports nothing and exports Fortress.IO. We generate these
components by compiling the source files:
compile("IronIO.fss")
compile("IronCrypto.fss")
The results are depicted diagrammatically in Figure 22.1.
Link A collection of one or more components exporting different APIs may be combined to form a new, compound,
component by calling the link operation, passing the names of the components to link along with the name of the
resulting compound component. Syntactically, a link operation is written as follows: 2
link(result:String, constituents:String...):()
The components being linked are called constituents of the resulting component, which exports all the APIs exported
by any of its constituents, and imports the APIs imported by at least one of its constituents but not exported by any of
them.
For example, we can link the IronIO and IronCrypto libraries compiled above:
link(IronLink, IronIO, IronCrypto)
The resulting component, illustrated in Figure 22.2, imports Fortress.Security and exports Fortress.IO and Fortress.Crypto.
link does not distinguish between simple and compound components, so we can get arbitrarily nested components.
For example, we can construct an application CoolCryptoApp by compiling another source code, IronSecurity.fss,
for the library IronSecurity that imports Fortress.IO and exports Fortress.Security, and then linking the result with
IronLink.
2 We present only the basic form of link here. link has additional optional arguments that we discuss in the Section 22.8.
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